Pipistrel on Fuel Vaporisation

Below is an excerpt from a letter circulated by Pipistrel :

"Date: 23th April 2024 Subject: Vapor lock preventive actions, applicable to all Pipistrel aircraft equipped with Rotax 912, 912 iS and 914 engine types

NOTE: Steps specified below act as additional content to the existing procedures outlined in the applicable aircraft flight manual.

BEFORE FLIGHT:

• If temperatures rise in the area of run-up, it is advised to increase RPM above idle in order to force more air through the engine compartment, which will maximize the cooling.

• If aircraft is equipped with auxiliary/booster fuel pump, pay attention to its sound – any significant “non-standard” deviation in pitch of the sound could indicate presence of the trapped vapor.

• After takeoff, reduce climb angle to increase airflow through the engine compartment, which will maximize the cooling.

AFTER FLIGHT:

• If situation permits, park the aircraft with nose pointing into the wind.

• Before shutdown, let the engine cool down at idling.

• Keep the doors opened – this will allow heat to escape from the cabin, which is especially beneficial at configurations with fuselage tank installed."

Not having access to the Pipistrel "flight manual" I don't know what additional information it may containe on the subject/management of fuel vaporisation - I am concerned that the above letter does not go nearly far enough in that it has failed to refer to:

• highlight the main/most likely time for this phenomena to occur, is on the ground, after flight, on a hot day 
• advise, opening any inspection doors/hatches to allow the hot air from heat soaked engine to escape more readily.
• mention symptoms, like low or even zero, fuel pressure indication (other than a vague reference to boost pump, if fitted, sound)
• another symptom: hot starting problems
• mitigation; the assistance a correctly fitted return fuel line will give in helping to minimise/alleviate this problem.
• the safety implications in not having a boost pump.
• techniques; the need  to run the boost pump until posative/acceptable fuel pressure is achieved - this may include during attempted start.
• extended run up time, to not only assess the engines condition but to further aid in clearing fuel vapour from the system.
• having a "plan" should the engine not deliver full power/die on take-off/climb out.

The advice to :

"..........let the engine cool down at idling." may not be good, in that most aircraft will taxi, inducing a flow of air through the cowling/cooling systems befor shut down. Further engine running while aircraft is stationary may only exacerbate the heating of under cowl component/fuel lines, leading to a greater chance of vaporisation. I would recomend stopping the engine as soon as aircraft has parked.

Keep the doors opened – this will allow heat to escape from the cabin, which is especially beneficial at configurations with fuselage tank installed."  - Will do no harm, sounds like BS to me. While it is desirable to keep all onboard fuel cool, the fuel stored in the tank(s) will not be influenced by the heat from the engine, which is the main generator/origin of the problem, often referred to as "vapour lock"

Note: Please read the whole letter  - there is more generalised information that you may find informative - https://raaus.com.au/wp-content/uploads/2024/05/PVS-2304_2024-Circular_letter.pdf